After several years of development, RM Propulsion has completed its test rig for testing stern tube seals.
Type approved Stern tube seal
In May this year the first test runs were successfully made in order to obtain the DNV Type Approval for RMS OCEAN SEAL. We have passed all these tests with flying colours.
Multifunctional test possibilities
Furthermore, we plan testing different sealing materials and the effects of bio degradable lubricants (EAL’s).
The test rig is best described as a vessel without a hull, accommodation, propeller or engine room. The only thing left is the stern tube, tail shaft and the FWD & AFT sealing system with its tanks.
Rather than having a simplified laboratory set-up with a test bench where you can test a single sealing ring, we decided to look at the real world on a vessel
Therefore, we engineered a complete stern tube with a full-size propeller shaft, driven by a large E-motor. The shaft is supported by 2 plain bearings at both ends of the oil filled stern tube. The shaft and stern tube are sealed by our OCEAN SEAL O2 FWD and OCEAN SEAL 04 AFT system. The AFT seal is submersed in seawater. As on most vessels the system is equipped with a FWD, and AFT seal monitoring tank and a Gravity Tank to supply the stern tube with oil. With air pressure we regulate the pressure of both the oil and the sea water to simulate the vessel’s draft or to simulate waves. With heaters and coolers, we can regulate the temperatures of the oil and seawater.
Leakages, (seal) temperatures, pressures, power consumption, rpm etc. are all recorded digitally. Different kind of tests can be executed fully automated, for example operation under heavy seas or misalignment conditions. This test rig allows us to test any seal size, under any realistic operating conditions.
We believe this test set-up simulates the actual operating conditions as closely as possible.
The process of developing this test rig was a challenging one and we experienced a number of issues during the built and the initial trial runs. At first, we underestimated the power needed to rotate the shaft at the required speed. When it was solved by a larger E-motor we managed to run the machine at full speed. Then we discovered that both the oil and water temperature ran out of control. So, a bigger cooler was needed as well as a serious upgrade of our electric power supply and a ventilation system to keep the ambient temperature at reasonable levels. Apart from these bigger challenges we faced minor problems related to alignment, thrust bearing damage and the inevitable smaller engineering, production or judgement errors. But fortunately, no problems were observed with the seals. Each modification took considerable time and money to engineer and manufacture, but finally we are happy with the result.
All in all a steep learning curve, but it is worthwhile because we now have all the possibilities to develop and test new products to meet the changing demands of the maritime industry.
Source: By Robin Mulders. Owner/CEO, RM Propulsion BV
